Memory device with timing overlap mode and precharge timing circuit

ABSTRACT

In some examples, a memory device is configured to receive a precharge command and an activate command. The memory device performs a first series of events related to the precharge command in response to receiving the precharge command and a second series of events related to the activate command in response to receiving the activate command. The memory device delays the start of the second series of events until the first series of events completes.

RELATED APPLICATION

This application is a continuation of, and claims priority to, U.S.application Ser. No. 14/595,568, filed on Jan. 13, 2015 now U.S. Pat.No. 9,230,633, entitled Memory Device With Timing Overlap Mode, whichclaims priority to U.S. Pat. No. 8,976,610, filed on Oct. 9, 2013,entitled Memory Device with Timing Overlap Mode, which claims priorityto U.S. Provisional Application No. 61/712,552 to Andre et al., entitled“tRP Overlap Mode,” filed Oct. 11, 2012, all of which are incorporatedherein by reference in their entirety.

BACKGROUND

In some types of memory devices, such as random access memories (RAM), apredetermined series of commands are received from a source attemptingto access the memory device. Following receipt of each command, a set ofoperations related to each of the commands are performed subject tostrict timing requirements with no overlap.

Unfortunately, the memory device has no control over when the commandsare received, as the commands are generated by the external source.Thus, the timing constraints of the memory device are designed to matchthe timing constraints of the external sources compatible with thememory device in order to avoid errors.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical components or features.

FIG. 1 illustrates select components of an example system including amemory device to receive a command while executing an operation,according to some implementations

FIG. 2 illustrates select components of another example system includinga memory device to receive a command while executing an operation,according to some implementations

FIG. 3 illustrates a timing diagram associated with the memory devicesof FIGS. 1 and 2, according to some implementations.

FIG. 4 illustrates an example flow diagram showing an illustrativeprocess for receiving overlapping commands, according to someimplementations.

FIG. 5 illustrates a partial flow diagram and a partial timing diagramshowing an illustrative process for receiving overlapping commands,according to some implementations.

DETAILED DESCRIPTION

This disclosure includes techniques and implementations to improveflexibility associated with performing read and write operations on amemory device. In some implementations, the memory device is configuredto receive an activate command from an external source, beforecompletion of operations associated with a precharge command. Forexample, in typical memory devices, a predetermined series of commandsand operations are received and performed in sequence to accomplish oneor more read and/or write operations. The series of commands andoperations include a precharge command and precharge operations to closean open page within the memory array (for instance, writing the contentsof the cache associated with a previous read or write operation to thememory array). The series of commands also includes an activate commandand activate operations to open a page in the memory array and load theassociated page to the cache and one or more read and/or write commandsto edit the contents of the page while stored in the cache.

Each of the operations are typically performed in sequence with nooverlap to avoid errors and/or collisions in the cache. The execution ofeach set of operations is also subject to timing requirements followingthe receipt of the corresponding command by the memory device. Ingeneral, an external source reading or writing data to the page firstissues the precharge command to the memory device and then waits for afirst period of time to elapse before issuing the activate command. Thisfirst period of time is typically referred to as row precharge time(tRP) and represents the number of clock cycles available to the memorydevice to complete the operations associated with the precharge command(i.e., the number of clock cycles between receiving the prechargecommand and receiving the activate command at the memory device).

After the first period of time elapses, the external source issues theactivate command which is received by the memory device. The externalsource then waits for a second period of time before issuing at leastone read or write command. This second period of time is typicallyreferred to as row address to column address delay (tRCD) and representsthe number of clock cycles available to the memory device to completethe operations associated with the activate command (i.e., the number ofclock cycles between receiving the activate command and receiving atleast one read or write command at the memory device).

As described above, the periods tRP and tRCD are governed by theexternal source accessing the memory device, as the external sourceaccessing the memory device issues the precharge, activate, andread/write commands. While many of the external sources includeregisters that may be used to program delays corresponding to the numberof clock cycles associated with the periods tRP and tRCD to betteraccommodate different types of memory devices, the delays are oftenlimited to a maximum number of clock cycles. Moreover, in some cases,the maximum number of clock cycles for one of the delays (tRP or tRCD)may be insufficient. In particular, magnetic random access memory (MRAM)devices may require more clock cycles to perform the prechargeoperations than other types of memory devices.

In some implementations, the memory devices described herein areconfigured to be able to receive an activate command from an externalsource, before completion of operations associated with the prechargecommand in order to increase the number of clock cycles available to thememory device to complete the precharge operations. For instances, thememory devices may be configured to utilize both the clock cyclesassigned to the time period tRP to perform the precharge operations andthe clock cycles assigned to the time period tRCD to perform theactivate operations as a combined time period tRP+tRCD to complete boththe precharge operations and the activate operations. For example, thememory device may include a command interpreter configured to receivethe precharge and activate commands, as well as, read and/or writecommands from one or more external sources. The memory device alsoincludes an overlap circuit (such as an AND gate) configured to delaythe execution of the operations associated with the activate commanduntil both the activate command and a completion signal from a prechargetiming circuit are received. In this manner, the memory device is ableto receive the activate command, while the operations associated withthe precharge command are still being performed. Thus, the presentdisclosure may allow the memory device to be utilized in a greaternumber of systems and to be accessed by additional types of externalsources.

In one example, tRP may be limited to a maximum number of 15 clockcycles, while tRCD may be limited to a maximum number of 200 clockcycles. In this example, assume that the memory device requires moreclock cycles than the maximum number of clock cycles associated with theperiod tRP to complete the precharge operations, for instance, 30 clockcycles, while less than the maximum number of clock cycles associatedwith the period tRCD to complete activate operations, for instance, 100clock cycles. Since the memory device requires 30 clock cycles tocomplete the precharge operations and 100 clock cycles to complete theactivate operations, the external source may be programmed or configuredto issue the precharge command to the memory device and to wait themaximum number of clock cycles, i.e., the 15 clock cycles before issuingthe activate command. The external source may also be programmed orconfigured to wait 115 clock cycles before issuing a read or writecommand, i.e., the 100 clock cycles necessary to perform the activateoperations and the remaining 15 clock cycles to finish the prechargeoperations.

In this example, the memory device may be configured to receive both theprecharge and activate commands, but to prevent the activate operationsfrom initiating until the precharge operations are complete. Forinstance, the memory device is able to receive the precharge command andbegin the precharge operations. At the 15th clock cycle, the memorydevice then receives the activate command and during the 30th clockcycle completes the precharge operations. Also during the 30th clockcycle, the memory device begins the activation operations, which arecompleted before the external source issues a read or write command atthe 130th clock cycle. In this way, the memory device has a total clockcycle period (tRP+tRCD) of 130 clock cycles to perform both theprecharge operations and the activation operations regardless of theindividual maximum timing constrains for tRP or tRCD imposed by theexternal source.

FIG. 1 illustrates select components of an example system 100 includinga memory device 102 able to receive a command while executing anoperation, according to some implementations. The memory device 102 isan example of tangible non-transitory computer storage media and mayinclude volatile and nonvolatile memory and/or removable andnon-removable media implemented in any type of technology for storage ofinformation such as computer-readable instructions or modules, datastructures, program modules or other data. Such computer-readable mediamay include, but is not limited to, RAM, ROM, EEPROM, flash memory orother computer-readable media technology, solid state storage, RAIDstorage systems, storage arrays, network attached storage, storage areanetworks, cloud storage, or any other medium that can be used to storeinformation. In one particular example, the memory device may be amagnetic memory or magnetic disk storage, such as an MRAM device.

The memory device 102 includes a command interpreter 104 configured toreceive commands 106 (e.g., precharge, activation, and read/writecommands) from at least one external source 108. The command interpreter104 is further configured to provide a received precharge command 110 toa precharge timing unit 112 for initiating events 114(1)-(N) associatedwith the precharge operations and to provide a received activate command116 to an activate timing unit 118 through overlap circuit 122 forinitiating events 120(1)-(N) associated with the activation operations.

The external source 108 may be a circuit of the system 100 which isconfigured to access (e.g., read from and/or write to) the memory device102. The external source 108 may be a general purpose processor, acentral processing unit, a graphical processing unit, or one or morecontrol circuits, among other possible circuits of the system 100. Insome cases, the external source 108 may include more than one processor,such as multi-core processors and/or multiple circuits.

The precharge timing unit 112 is configured to control the start of eachof the events 114(1)-(N) associated with one or more of operationsrelated to the precharge command 110. For example, the precharge timingunit 112 may be configured to detect a precharge command 110 and, inresponse, to initiate event 114(1), wait for a first predetermined delayto elapse, and, in response, to initiate event 114(2). The prechargetiming unit 112 then waits for a second predetermined delay to elapseand, in response, initiates event 114(3), and so forth. In someimplementations, each of the predetermined delays may be the sameduration. In other implementations, the time associated with the firstpredetermined delay may vary from the time associated with the secondpredetermined delay. For instance, the duration of the firstpredetermined delay may be related to the type of operations performedduring event 114(1), while the duration of the second predetermineddelay may be related to the type of operations performed during event114(2).

The events 114(1)-(N) are a sequence of operations initiated by theprecharge timing unit 112 for closing an open page in the memory device102. For instance, the memory device 102 may be configured to performrow operations and to read an entire page (or row) from one of thememory banks (or arrays) and store the page in a cache, such thatmultiple read and/or write operations may be issued from the externalsource 108 to edit or update the contents of the page. In this instance,the events 114(1)-(N) associated with the precharge operations may causethe page currently stored in the cache to be written back to the memorybank (or array) from which the page (or row) was originally read inorder to preserve changes made to the page while the page was stored inthe cache. For example, the events 114(1)-(N) may be operationsassociated with setting a word line voltage level, a column selectoperation, a write back operation, or a word line and/or column selectdisable.

The activate timing unit 118 is configured to control the start of eachof the events 120(1)-(N) associated with one or more of the activateoperations. For example, the activate timing unit 118 may be configuredto detect an activate command 116 and, in response, to initiate event120(1), wait for a first predetermined delay to elapse and, in response,to initiate event 120(2). The activate timing unit 118 then waits for asecond predetermined delay to elapse and, in response, initiates event120(3), and so forth. In some implementations, each of the predetermineddelays may be the same duration. In other implementations, the timeassociated with the first predetermined delay may vary from the timeassociated with the second predetermined delay. For instance, theduration of the first predetermined delay may be related to the type ofoperations performed during event 120(1) and the duration of the secondpredetermined delay may be related to the type of operations performedduring event 120(2).

The events 120(1)-(N) are a sequence of operations initiated by theactivate timing unit 118 for loading a page (or row) into the cache ofthe memory device 102 prior to the command interpreter 104 receiving aread/write command associated with the page. For instance, as discussedabove, the memory device 102 may be configured to perform row operationsto read an entire page (or row) from one of the memory banks (or arrays)and store the page in a cache. In this instance, the events 120(1)-(N)associated with the activation operations may cause the memory device102 to load a new page (or row) into the cache. For example, the events120(1)-(N) may be associated with setting a word line voltage level, acolumn select operation, a read sample operation, applying a resetvoltage to a bit line or source line, read evaluate operation, or a wordline and/or column select disable operation.

The memory device 102 also includes an overlap circuit 122. The overlapcircuit 122 receives the activate command 116 from the commandinterpreter 104 and a completion signal 124 from the precharge timingunit 112 following the completion of the last event 114(N) associatedwith the precharge command 110. The overlap circuit 122 is configured toprevent the activate timing unit 118 from initiating the events120(1)-(N) associated with the activate operations until the events114(1)-(N) associated with the precharge command 110 have been completedand the activate command 116 is received from the external source 108.For example, the overlap circuit 122 may be an AND gate that activatesupon the receipt of both the activate command 116 and the completionsignal 124.

In some implementations, the completion signal 124 is generated by theprecharge timing unit 112 upon the expiration of a predetermined delayassociated with the last event 114(N). In other implementations, theprecharge timing unit 112 may not generate the completion signal 124directly, rather the completion signal 124 may be generated as part ofevent 114(N).

In general, when the external source 108 attempts to read data from orwrite data to the memory device 102, the external source 108 issues theprecharge command 110 and waits for a predetermined number of clockcycles associated with a period tRP. The command interpreter 104 of thememory device 102 receives the precharge command 110 and starts theassociated precharge operations by providing the precharge command 110to the precharge timing unit 112.

The precharge timing unit 112 initiates events 114(1)-(N) based on clocksignals and predetermined delays associated with each of the events114(1)-(N). In some instances, the first period tRP expires before theevents 114(1)-(N) are completed and the external source 108 issues theactivate command 116 and proceeds to wait a number of clock cyclesassociated with a second period tRCD. For example, the first period tRPmay be set to a maximum of 15 clock cycles but the events 114(1)-(N)require up to 30 clock cycles to complete. In this instance, the commandinterpreter 104 provides the activate command 116 to the overlap circuit122. However, the overlap circuit 122 does not cause the activate timingunit 118 to initiate events 120(1)-(N) associated with the activateoperations until the overlap circuit 122 receives the completion signal124 from the precharge timing unit 112.

The precharge timing unit 112 continues to start events 114(1)-(N) untileach of the events 114(1)-(N) have finished. After the events havefinished, the precharge timing unit 112 provides the completion signal124 to the overlap circuit 122. For instance, the overlap circuit 122may receive the completion signal 124 following the 30th clock cycle(i.e., the number of clock cycles required to complete the prechargeoperations in the example above). Once the overlap circuit 122 receivesthe completion signal 124 and the activation command 116, the overlapcircuit 122 causes the activate timing unit 118 to initiate events120(1)-(N).

At some time after the events 120(1)-(N) are completed, the externalsource 108 begins to issue read and write commands related to the pageloaded into the cache during the execution of the activate operations.For example, the second period tRCD may be set to 130 clock cycles andthe events 120(1)-(N) may require 100 clock cycles to complete. In thisexample, the external source 108 waits a total of 145 clock cycles afterthe precharge command before issuing a read or write command. During the145 clock cycles, the events 114(1)-(N) are performed utilizing thefirst 30 clock cycles and the events 120(1)-(N) are performed utilizingthe next 100 clock cycles. Thus, in this example, 130 clock cycles ofthe 145 clock cycles are utilized to perform the precharge and activateoperations in order to prepare the cache of the memory device 102 forreceiving read and write accesses.

Therefore, it should be understood that by incorporating the overlapcircuit 122 into the memory device 102, the memory device 102 is able toallocate the clock cycles associated with both the first and secondperiods (tRP+tRCD) to either the precharge operations or the activateoperations, thereby increasing the number of external sources 108 thatmay utilize the particular memory device 102.

FIG. 2 illustrates select components of another example system 200including a memory device 202 able to receive a command while executingan operation according to some implementations. The memory device 202includes a command interpreter 204 configured to receive commands 206(e.g., precharge, activation, and read/write commands) from an externalsource 208 (e.g., a processor or control circuit). The commandinterpreter 204 is further configured to provide a precharge command 210to a precharge timing unit 212 for processing events 214(1)-(N)associated with the precharge operations and to provide the activatecommand 216 to an activate timing unit 218 through an overlap circuit208 for processing events 220(1)-(N) associated with the activationoperations.

The external source 208 is a circuit of the system 200 that may beconfigured to access (e.g., read from and/or write to) the memory device202. The external source 208 may be a general purpose processor, acentral processing unit, a graphical processing unit, or one or morecontrol circuits, among other possible circuits of the system 200. Insome cases, the external source 208 may include more than one processor,such as multi-core processors and/or multiple circuits.

The precharge timing unit 212 is configured to control the start of eachof the events 214(1)-(N) associated with one or more operations relatedto the precharge command 210. For example, the precharge timing unit 212may be configured to detect a precharge command 210 and, in response, toinitiate event 214(1), wait for a first predetermined delay to elapseand, in response, to initiate event 214(2). The precharge timing unit212 then waits for a second predetermined delay to elapse and, inresponse, initiates event 214(3), and so forth. In some implementations,each of the predetermined delays may be the same duration. In otherimplementations, the time associated with the first predetermined delaymay vary from the time associated with the second predetermined delay.For instance, the duration of the first predetermined delay may berelated to the type of operations performed during event 214(1), whileduration of the second predetermined delay may be related to the type ofoperations performed during event 214(2).

The events 214(1)-(N) are a sequence of operations initiated by theprecharge timing unit 212 for closing an open page in the memory device102. For instance, the memory device 202 may be configured to performrow operations to read an entire page (or row) from one of the memorybanks (or arrays) and store the page in a cache, such that multiple readand/or write operations associated with the page may be issued from theexternal source 208. In this instance, the events 214(1)-(N) associatedwith the precharge operations may cause the page currently stored in thecache to be written back to the memory bank from which the page (or row)was originally read to preserve changes made while the page was storedin the cache. For example, the events 214(1)-(N) may be associated withsetting a word line voltage level, a column select operation, a writeback operation, or a word line and/or column select disable.

The activate timing unit 218 is configured to control the start of eachof the events 220(1)-(N) associated with one or more of the activateoperations. For example, the activate timing unit 218 may be configuredto detect an activate command and, in response, to initiate event220(1), wait for a first predetermined delay to elapse and, in response,to initiate event 220(2). The activate timing unit 218 then waits for asecond predetermined delay to elapse and, in response, initiates event220(3), and so forth. In some implementations, each of the predetermineddelays may be the same duration. In other implementations, the durationof the first predetermined delay may vary from the duration of thesecond predetermined delay. For instance, the duration of the firstpredetermined delay may be related to the type of operationscorresponding to the event 220(1) and the duration of the secondpredetermined delay may be related to the type of operationscorresponding to the event 220(2).

The events 220(1)-(N) are a sequence of operations initiated by theactivate timing unit 218 for loading a page (or row) into the cache ofthe memory device 202 prior to the command interpreter 204 receiving aread/write command. For instance, as discussed above, the memory devicemay be configured to perform row operations to read an entire page (orrow) from one of the memory banks (or arrays) and store the page in acache. In this instance, the events 220(1)-(N) associated with theactivation operations may cause the memory device 202 to load a new page(or row) into the cache. For example, the events 220(1)-(N) may beassociated with setting a word line voltage level, a column selectoperation, a read sample operation, applying a reset voltage to a bitline or source line, read evaluate operation, or a word line and/orcolumn select disable operation.

In the example of FIG. 2, the memory device 202 also includes an OR gate226. The OR gate 226 is configured to generate a ready signal 228 inresponse to receiving either an enable signal 230 from an enable circuit232 or a completion signal 224 from the precharge timing unit 212. Thecompletion signal 224 indicates that the last of the events 214(1)-(N)is complete, while the enable signal 230 is utilized as an override tostart the events 220(1)-(N) associated with the activate operationsearlier than would be the case in the memory device 102 of FIG. 1. Insome implementations, the enable circuit 232 is incorporated into thememory device 202, while in others the enable circuit 232 is an externalcircuit, as illustrated in FIG. 2.

The memory device 202 also includes an overlap circuit 222 that receivesthe ready signal 228 from the OR gate 226. The overlap circuit 222 alsoreceives the activate command 216 from the command interpreter 204. Theoverlap circuit 122 is configured to prevent the activate timing unit218 from initiating the events 220(1)-(N) associated with the activateoperations until events 214(1)-(N) are complete or the enable circuit232 provides the enable signal 230 (e.g., an override signal) and theactivate command 216 has been received from the external source 208. Forexample, the overlap circuit 222 may be an AND gate that activates uponthe receipt of both the activate command 216 and the ready signal 228.

In general, for the external source 208 to read data from or write datato the memory device 202, the external source 208 issues the prechargecommand 210 and waits a number of clock cycles assigned to a firstperiod tRP. The command interpreter 204 of the memory device 202receives the precharge command 210 and initiates the prechargeoperations by providing the precharge command 210 to the prechargetiming unit 212.

The precharge timing unit 212 initiates events 214(1)-(N) based on clocksignals and predetermined delays associated with each of the events214(1)-(N). In some instances, the first period tRP expires before theevents 214(1)-(N) are completed and the external source 208 issues theactivate command 216 and a number of clock cycles assigned to a secondperiod tRCD. For example, the first period tRP may be set to a maximumof 30 clock cycles but the events 214(1)-(N) require 45 clock cycles tocomplete. In this instance, the command interpreter 204 provides theactivate command 216 to the overlap circuit 222. However, the overlapcircuit 222 does not cause the activate timing unit 218 to begin events220(1)-(N) associated with the activate operations, as the ready signal228 has not been received from the OR gate 226.

The OR gate 226 provides the ready signal 228 upon either receiving thecompletion signal 224 from the precharge timing unit 212 following thecompletion of the events 214(1)-(N) or upon receiving the enable signal230. Once the OR gate 226 provides the overlap circuit 222 the readysignal 228, the overlap circuit 222 causes the activate timing unit 218to begin the events 220(1)-(N) when the activate command 216 has beenreceived.

Sometime after the events 220(1)-(N) are completed, the external source208 begins to issue read and write commands related to the page loadedinto the cache during the execution of the activate operations. Forexample, the second period tRCD may be set to 115 clock cycles and theevents 220(1)-(N) may require 100 clock cycles to complete. In thisexample, the external source 208 waits 145 clock cycles after theprecharge command before issuing a read or write command. During the 145clock cycles, the events 214(1)-(N) are performed utilizing the first 45clock cycles and the events 220(1)-(N) are performed utilizing the next100 clock cycles. Thus, in this example, the memory device 202 is ableto perform each event related to the precharge operations and each eventrated to the activate operations without causing collisions in the cacheor other errors, even though the period tRP is insufficient forperforming operations associated with events 114(1)-(N).

Therefore, it should be understood that by incorporating the overlapcircuit 222 into the memory device 202, the memory device 202 is able toallocate the clock cycles associated with both the first period tRP andsecond periods tRCD as a combined period tRP+tRCD to either theprecharge operations or the activate operations increasing theflexibility available to the memory device manufactures.

FIGS. 1 and 2 provides example architectures for memory devicesassociating to some implementations. FIG. 3 provides a timing diagram tobetter illustrate the operations associated with the precharge command,the activate command, and at least one read or write command.

FIG. 3 illustrates a timing diagram 300 associated with a memory device,such as memory devices 102 and 202 of FIGS. 1 and 2 according to someimplementations. The timing diagram 300 illustrates events associatedwith an external source accessing one page of data stored in the memorydevice from the perspective of the memory device. The timing diagram 300is illustrated based on clock cycles and includes illustrated clockcycles 302-316. It should be understood that a length of time betweeneach of the clock cycles and a total number of clock cycles is animplementation detail and that, as illustrated, additional clock cyclesmay exist between clock cycles 304 and 306, clock cycles 308 and 310,and clock cycles 312 and 314.

In the illustrated example, the memory device is configured to utilizethe combined period tRP+tRCD (illustrated as 326 and 328, respectively)to complete both the internal precharge operations 318 and the internalactivate operations 320, while avoiding collisions in the cache andother errors. As illustrated, the memory device receives the prechargecommand 322 from the external source on the rising edge of clock cycle304. In response, the memory device begins to perform internal prechargeoperations 318 (e.g., events 114(1)-(N) and 214(1)-(N) of FIGS. 1 and2). Receipt of the precharge command 322 also starts the period tRP 326(i.e., the number of clock cycles the external source waits beforeissuing the activate command 324). As illustrated, the internalprecharge operations 318 are not complete until the clock cycle 308 andthe activate command 324 is received following the expiration of theperiod tRP 326, during clock cycle 306.

However, rather than starting the internal activate operations 320 inresponse to receiving the activate command 324, the memory device delaysthe start of the internal activate operations 320 until the internalprecharge operations 318 are completed (i.e., during clock cycle 308).For example, the memory device may be equipped with an AND gate whichcontrols the execution of the internal activate operations 320 based onboth the activate command 324 and a completion signal associated withthe internal precharge operations 318. In this way, the memory device isable to avoid a collision that would otherwise result from the internalprecharge operations 318 writing a first page stored in the cache of thememory device to one of the memory banks (or arrays), while the internalactivate operations 320 are writing a second page from another one ofthe memory banks (or arrays) into the cache, as the activate command 324is received prior to the completion of the internal precharge operations318.

When the activate command 324 is received, the period tRCD 328 that theexternal source waits before issuing a read/write command 330 begins.During the period tRCD 328, the internal precharge operations 318 arecompleted and, upon completion of the internal precharge operations 318(during clock cycle 308), the internal activate operations 320 areinitiated. In the illustrated example, the read/write command 330 isreceived on the rising edge of clock cycle 312. However, as illustratedin FIG. 3, the internal activate operations 320 are not complete withinthe period tRCD 328. The extension of the internal activate operations320 past the period tRCD 328 illustrates the fact that the memory devicemay experience a short delay between receiving the internal read/writecommand 330 and beginning the read/write operation 332.

FIGS. 4 and 5 are flow diagrams illustrating example processes of memorydevices capable of receiving overlapping commands. The processes areillustrated as a collection of blocks in a logical flow diagram, whichrepresent a sequence of operations, some or all of which can beimplemented in hardware, software or a combination thereof. In thecontext of software, the blocks represent computer-executableinstructions stored on one or more computer-readable media that, whichwhen executed by one or more processors, perform the recited operations.Generally, computer-executable instructions include routines, programs,objects, components, data structures and the like that performparticular functions or implement particular abstract data types.

The order in which the operations are described should not be construedas a limitation. Any number of the described blocks can be combined inany order and/or in parallel to implement the process, or alternativeprocesses, and not all of the blocks need be executed. For discussionpurposes, the processes herein are described with reference to theframeworks, architectures and environments described in the examplesherein, although the processes may be implemented in a wide variety ofother frameworks, architectures or environments.

FIG. 4 illustrates an example flow diagram showing an illustrativeprocess 400 for applying overlapping commands, according to someimplementations. At 402, a precharge command is applied to a memorydevice (such as the memory devices 102 and 202 of FIGS. 1 and 2), forinstance, from an external source (e.g. the external sources 108 and 208of FIGS. 1 and 2). In general, when the memory device receives theprecharge command, the memory device performs the precharge operationsor the operations associated with closing an open page in the memorydevice. For example, the memory device may perform one or moreoperations associated with writing the contents of the cache to a memorybank (or array) of the memory device in order to save changes made tothe page while stored in the cache.

At 404, an activate command is applied to the memory device, forinstance, from the external source. In general, when the memory devicereceives the activate command, the memory device performs the activateoperations or the operations associated with reading a page to the cacheof the memory device. For example, the memory device may perform one ormore operations associated with selecting a row (or page) from a memorybank (or array) and writing the contents of the row to the cache.

At 406, the memory device waits at least a number of clock cyclestRP+tRCD to expire. For example, in the memory device describe herein,the memory device utilizes the combined period tRP+tRCD to perform boththe precharge operations and the activate operations, rather thanutilizing the period tRP for the precharge operations and the periodtRCD for the activate operations. For example, the memory device mayrequire 30 clock cycles to complete the precharge operations and 100clock cycles to complete the activate operations. The external sourceaccessing the memory device, however, may be programmed to wait themaximum number of 15 clock cycles before issuing the activation commandand 115 clock cycles before issuing a read or write command. The memorydevice is configured to receive both the precharge and activatecommands, but to delay the activate operations until the prechargeoperations are complete. In this way, the memory device has a total of130 clock cycles or the period tRP+tRCD to perform both the prechargeoperations and the activation operations even though the activationcommand is received before the completion of the precharge operations.In other words, the memory device is able to receive the prechargecommand, begin the precharge operations, receive the activation commandfollowing the end of the 15th clock cycle, complete the prechargeoperations, and following the end of the 30th clock cycle, begin theactivation operations.

As shown at 408, a read command or, as shown at 410, a write command maybe applied to the memory devices, for instance, from the externalsource. For example, if the external source is attempting to read datafrom the memory device, the external source applies a read command 408and the memory device performs the read operation to read the requesteddata from the cache. If, however, the external source is attempting towrite data to the memory device, the external source applies a writecommand 410 and the memory device performs the write operation to writethe requested data into the cache.

FIG. 5 illustrates a partial flow diagram and partial timing diagramshowing an illustrative process 500 for receiving overlapping commands,according to some implementations. At 502, a memory device (such as thememory devices 102 and 202 of FIGS. 1 and 2) receives a prechargecommand from an external source (e.g., the external sources 108 and 208of FIGS. 1 and 2). In general, when the memory device receives theprecharge command, the memory device performs the precharge operationsor the operations associated with closing an open page in the memorydevice. For example, the memory device may perform one or moreoperations associated with writing the contents of the cache to a memorybank (or array) of the memory device in order to save changes made tothe page while stored in the cache.

At the time the precharge command is received by the memory device, afirst period tRP begins, as illustrated in FIG. 5. As described above,the period tRP is the number of clock cycles that the external sourcewaits before issuing the activate command to the memory device or thenumber of clock cycles that are typically available to the memory deviceto complete the precharge operations (e.g., events 114(1)-(N) or events214(1)-(N) of FIGS. 1 and 2).

At 504, a memory device receives an activate command from the externalsource. In general, when the memory device receives the activatecommand, the memory device performs the activate operations or theoperations associated with writing a page to the cache of the memorydevice. For example, the memory device may perform one or moreoperations associated with selecting a row (or page) from a memory bank(or array) and writing the contents of the row to the cache. However, asillustrated in the example of FIG. 5, the memory device receives theactivate command following the expiration of the period tRP but beforethe memory device completes the internal precharge operations (at 506).

At the time the activate command is received by the memory device, asecond period tRCD begins, as illustrated in FIG. 5. As described above,the period tRCD is the number of clock cycles that the external sourcewaits before issuing a read or write command to the memory device or thenumber of clock cycles available to the memory device to complete theactivate operations (e.g., events 120(1)-(N) or events 220(1)-(N) ofFIGS. 1 and 2).

At 506, the memory device completes the internal precharge operations.Since the activate command was received prior to the completion of theinternal precharge operations, when the memory device completes theinternal precharge operations, the memory device begins the internalactivation operations. Thus, in the illustrated example, the memorydevice utilizes the period tRP as well as part of the period tRCD toperform the internal precharge operations. By waiting to start theinternal activate operations until the completion of the internalprecharge operations, both the precharge operations and the activateoperations may be performed without an error occurring in the memorydevice.

At 508, the memory device completes the internal activate operations. Inthe illustrated example, the internal activate operations complete whenthe period tRCD expires. However, in other examples, the internalactivate operations may complete before the expiration of the periodtRCD. In this manner, the memory device is able to utilize the combinedperiod tRP+tRCD as desired to complete the internal precharge operationsand the internal activate operations. For example, the memory device isable to cause the internal precharge operations to overlap into theperiod tRCD, typically reserved for the internal activate operations.

Although the subject matter has been described in language specific tostructural features, it is to be understood that the subject matterdefined in the appended claims is not necessarily limited to thespecific features described. Rather, the specific features are disclosedas illustrative forms of implementing the claims.

What is claimed is:
 1. A memory device comprising: a circuit to receivea first command to cause the circuit to perform a first operation and asecond command to cause the circuit to perform a second operation;wherein the first operation and the second operation are completed bythe circuit prior to an expiration of a period of time, the period oftime representing a number of clock cycles that an external source waitsafter providing the first command plus a number of clock cycles theexternal source waits after providing the second command.
 2. The memorydevice as recited in claim 1, wherein the circuit includes: a prechargetiming circuit to perform the first operation; an activate timingcircuit to perform the second operation; and an overlap circuit to delayan initiation of the second operation until a completion of the firstoperation.
 3. The memory device as recited in claim 2, wherein theactivate timing circuit causes the memory device to load a new page ofdata stored in the memory device into a cache of the memory device. 4.The memory device as recited in claim 3, wherein: the number of clockcycles that the external source waits after providing the first commandis a period associated with a row-precharge-time; and the number ofclock cycles that the external source waits after providing the secondcommand is a period associated with a row-address-to-column-addressdelay.
 5. The memory device as recited in claim 3, wherein the activatetiming circuit causes the memory device to load a new page of datastored in the memory device into a cache of the memory device byinitiating a sequence of operations that includes a read sampleoperation, applying a reset voltage to a bit line or a source line, anda read evaluate operation.
 6. The memory device as recited in claim 1,wherein the circuit includes: an overlap circuit to delay an initiationof the second operation until a completion of the first operation; andwherein: the first operation is related to writing content of a cache ofthe memory device into a memory bank of the memory device; and thesecond operation is related to writing content of the memory bank of thememory device into the cache of the memory device.
 7. The memory deviceas recited in claim 1, wherein: the first operation is related towriting content of a cache associated with of the memory device into amemory bank of the memory device; and the memory device is a magneticrandom access memory that requires more clock cycles to perform thefirst operation than the number of clock cycles that the external sourcewaits after providing the first command.
 8. A system comprising: acircuit to generate a first command and a second command, the firstcommand and the second command associated with accessing data; and amemory device to store the data, the memory device to, at least in partin response to receiving the first command, initiate a first operationassociated with the first command and to temporarily prevent aninitiation of a second operation associated the second command.
 9. Thesystem as recited in claim 8, wherein the memory device includes acache, and wherein the first operation is associated with writingcontents of the cache into an associated page in a memory array of thememory device.
 10. The system as recited in claim 9, wherein the memorydevice is a magnetic memory device that requires more clock cycles toperform the first operation than the circuit waits after providing thefirst command to the memory device before the circuit provides thesecond command to the memory device.
 11. The system as recited in claim10, wherein the first command is a precharge command and the secondcommand is an activate command, wherein the second operation isassociated with loading a page of data from the memory array into thecache.
 12. The system as recited in claim 8, wherein the memory deviceinitiates the second operation at least in part in response to acompletion of the first operation.
 13. The system as recited in claim 8,further comprising an enable circuit coupled to the memory device, theenable circuit to generate an override signal to cause the memory deviceto initiate the second operation prior to the completion of the firstoperation.
 14. The system as recited in claim 8, wherein the circuit isa memory controller coupled to the memory device, wherein the memorycontroller has a programmed hardware configuration such that, after thememory controller applies the first command to the memory device, thememory controller applies the second command to the memory device beforethe memory device completes the first operation.
 15. A methodcomprising: receiving, at a circuit, a command from an external source,the command associated with accessing data stored in a memory device;generating, by the circuit, a control signal to at least in partinitiate a series of events related to the command; receiving, at thecircuit, an additional command; receiving, at the circuit, a signalindicating a completion of the series of events related to the command;and generating, by the circuit, an additional control signal to at leastin part initiate an additional series of events related to theadditional command.
 16. The method as recited in claim 15, wherein thecommand is a precharge command and the additional command is an activatecommand.
 17. The method as recited in claim 15, wherein the generatingof the additional control signal is at least in part in response to thereceiving of the signal indicating the completion of the series ofevents related to the command.
 18. The method as recited in claim 15,further comprising: providing the control signal to a second circuit,the second circuit to initiate the series of events related to thecommand; and providing the additional control signal to a third circuit,the third circuit to initiate the additional series of events related tothe additional command.
 19. The method as recited in claim 15, furthercomprising: providing the control signal to a second circuit, the secondcircuit to initiate the series of events related to the command; andproviding the additional control signal to the second circuit, thesecond circuit to initiate the additional series of events related tothe additional command.
 20. The method as recited in claim 15, furthercomprising: receiving, at the circuit, an override signal; and whereinthe generating of the additional control signal is at least in part inresponse to receiving the override signal.